How to Use a Cyclotron Particle Accelerator to Fight Cancer

How do you you target radiation treatments to kill only cancer cells? First, build a particle accelerator. Second: Aim carefully. Here's how the University of Pennsylvania's $144 million "smart bomb" cyclotron works.

Step 1

CYCLOTRON

Step 2

BEAM LINE

Protons moving at almost the speed of light are deflected and focused by magnets along the line. The beam lines are kept in a vacuum so that the particles don't slow down. The line branches to up to five separate treatment rooms.

Step 3

GANTRIES

These 90-ton machines aim the proton beam at the patient's body; the relatively heavy particles slow down when they encounter body tissue. When they move more slowly they interact with atoms in the body, producing ionizing radiation. Doctors can adjust the strength of the beam to cause the protons to produce radiation only at the tumor's location.

Radiation treatments for cancer are double-edged swords: They indiscriminately destroy healthy tissue along with cancer cells, causing debilitating side effects. To target cancer cells alone, the University of Pennsylvania is opening a next-generation treatment facility that uses high-energy proton beams to deliver pinpoint strikes.

Penn's $144 million Roberts Proton Therapy Center will use magnets to accelerate protons to near light speed in a 220-ton cyclotron. The beam lines direct the proton beams into treatment rooms where patients will have their tumors zapped. Nozzles on the ends of 90-ton gantries, aided by the CT, MRI and PET imaging equipment, aim the beams. The proton beam works like any other form of ionizing radiation, which destroys cancer cell DNA and prevents replication. "The difference is all in the physical characteristics of the beam itself," explains James Metz, chief of clinical operations of the new facility. "A regular X-ray goes in one side of the body and out the other side and irradiates everything in between." But unlike the massless photons that compose X-rays, protons are heavy particles that enter the body without much scattering, so they can be aimed with precision. They also continue in a straight line as they slow, releasing radioactive energy at a location determined by the beam's energy. "What that means for the patient is a much lower dose in front of the tumor and absolutely no radiation behind the tumor," Metz says.

The Roberts Center has announced partnerships with the Children's Hospital of Philadelphia, Walter Reed Army Medical Center and Bethesda's National Naval Medical Center to increase access to the expensive treatment offered by the new facility.